The present invention relates generally to the manufacture of high density tungsten alloy sheet, and more particularly, to a method of producing such an alloy sheet product by first forming a thin sheet or foil substrate of a first alloy constituent or a mixture of alloy constituents and partially sintering a mixture of tungsten powder and a second alloy constituent powder thereon. Densification is by solid diffusion bonding and subsequently by liquid phase infiltration of the sheet or foil substrate into the tungsten alloy skeleton.
There is presently a need for substantial quantities of high density tungsten alloy in sheet form for such applications as aircraft components, radiation screens and shields in radiation detectors and the like. Unfortunately, full development of the application potentials for these products is being inhibited by the extremely high cost of manufacturing when using conventional press-liquid phase sinter-powder metallurgy techniques. Commonly used powder metallurgy processes are most cost effective in the production of relatively small components by pressing the metal powder mixture, usually by the isostatic technique, to a shape that nearly approximates the finished part so as to minimize the expense of further working or machining operations. It is also known in the art to make relatively large powder pressings to form compacted billets that are then sintered and subsequently rolled, pressed or otherwise worked into the required shape and size. This technique has been employed in the manufacture of sheet material but it has been found that high density tungsten alloys work harden very rapidly which necessarily requires costly multiple, high temperature anneals to reach a significant reduction in area and prepare sheets of a reasonable size. In an effort to minimize these costly procedures, it is known to press powder compacts with increased plan form dimensions and reduced thickness in order to thereby reduce the number of roll-anneal cycles necessary to reach the desired finished sheet dimensions. Unfortunately, economic limitations are quickly reached in this method of sheet manufacture, in that the increased load capacity of the compacting press causes a more rapid increase in investment costs and also results in a generally slower rate of operation. Additionally, and, perhaps, more serious is the increased difficulty experienced in material handling when transferring the large, fragile pressed compacts from the mold cavities to the densification or sinter furnace. Excess scrap generation and slow production rates are common drawbacks inherent in this press-sinter method of sheet manufacture. Attempts to add temporary binders to increase the strength of the "green" (un-sintered) pressed compacts has proved unsatisfactory due to the fact that the binder tends to poison the tungsten alloy by destroying ductility.